riscv: s64ilp32: Correct the rv64ilp32 stackframe layout

The callee saved fp & ra are xlen size, not long size. This patch
corrects the layout for the struct stackframe.

echo c > /proc/sysrq-trigger

Before the patch:

sysrq: Trigger a crash
Kernel panic - not syncing: sysrq triggered crash
CPU: 0 PID: 102 Comm: sh Not tainted 6.3.0-rc1-00084-g9e2ba938797e-dirty #2
Hardware name: riscv-virtio,qemu (DT)
Call Trace:
---[ end Kernel panic - not syncing: sysrq triggered crash ]---

After the patch:

sysrq: Trigger a crash
Kernel panic - not syncing: sysrq triggered crash
CPU: 0 PID: 102 Comm: sh Not tainted 6.3.0-rc1-00084-g9e2ba938797e-dirty #1
Hardware name: riscv-virtio,qemu (DT)
Call Trace:
[<c00050c8>] dump_backtrace+0x1e/0x26
[<c086dcae>] show_stack+0x2e/0x3c
[<c0878e00>] dump_stack_lvl+0x40/0x5a
[<c0878e30>] dump_stack+0x16/0x1e
[<c086df7c>] panic+0x10c/0x2a8
[<c04f4c1e>] sysrq_reset_seq_param_set+0x0/0x76
[<c04f52cc>] __handle_sysrq+0x9c/0x19c
[<c04f5946>] write_sysrq_trigger+0x64/0x78
[<c020c7f6>] proc_reg_write+0x4a/0xa2
[<c01acf0a>] vfs_write+0xac/0x308
[<c01ad2b8>] ksys_write+0x62/0xda
[<c01ad33e>] sys_write+0xe/0x16
[<c0879860>] do_trap_ecall_u+0xd8/0xda
[<c00037de>] ret_from_exception+0x0/0x66
---[ end Kernel panic - not syncing: sysrq triggered crash ]---

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>